PROJECT SUMMARY/ ABSTRACT More than 50 million people over the age of 65 are currently affected by vascular cognitive impairment and dementia (VCID). Although the specific mechanisms for aging- induced VCID are not yet known, there is increasing evidence that alterations of the neurovascular unit play a crucial role. The objective of this proposal is to elucidate the mechanistic role of senescence-related endothelial dysfunction in cognitive impairment. The central hypothesis is that aging primarily promotes endothelial senescence in the brain and subsequent dysfunction, altering the production of vasodilator mediators, impairing neurovascular coupling responses, promoting blood-brain barrier (BBB) disruption and microvascular rarefaction. The resulting decline in cerebral blood flow (CBF) and increased neuroinflammation contribute to cognitive impairment. The proposed work is novel as it will be the first to demonstrate that aging-induced endothelial senescence is a critical contributing factor to the pathogenesis of VCID. The results will likely identify specific mechanisms and reveal potential therapies that are capable of improving CBF and restoring learning and memory. The following aims are proposed: 1) Determine how endothelial senescence alters neurovascular coupling responses, CBF and cognition in aging. The working hypothesis is that aging-induced activation of p16-dependent cellular senescence program in endothelial cells impairs vasodilator function. It is predicted that elimination of senescent endothelial cells, through genetic manipulation or through senolytic therapies will restore neurovascular function and improve CBF and cognition in aged mice. 2) Determine how senescence alters microvascular density and BBB integrity in aging. The working hypothesis is that activation of p16-dependent cellular senescence program in endothelial cells impairs endothelial barrier function and compromise the maintenance of the microcirculatory network. It is predicted that elimination of senescent cells will restore BBB, attenuating neuroinflammation and increase cerebromicrovascular density in aged mice. 3) Determine cellular heterogeneity among senescent endothelial cells in conjunction with their morphological and functional characteristics. Together, the proposed studies will identify a fundamental mechanism governing aging-induced cerebrovascular changes eventually leading to cognitive impairment.